For the operation of a circuit breaker, such as a medium voltage vacuum circuit breaker, it can be necessary to generate a high force to press the first moving electrical contact to a second corresponding fixed electrical contact. The force can be generated by a magnetic actuator. The magnetic actuator includes a coil for generating an electrical field, a core for forming this field, and a first movable plate which is attracted by the core. When being attracted by the core, the movable plate generates the force used for closing the circuit breaker.
WO 01/46968 A1 discloses a variable reluctance solenoid which includes an armature and a yoke located axially beyond one end of the armature. Magnetic attraction across an axial gap between the armature and yoke causes the armature to move axially and close the gap. The armature includes ferromagnetic laminations lying in a plane perpendicular to the axial direction. These laminations can include slots, proportioned and directed to combat eddy currents and reduce moving mass while avoiding the creation of flux bottlenecks. The solenoid can have two yokes on opposite sides of the armature, providing reciprocating armature motion.
EP 1 843 375 A1 discloses an electro-magnetic actuator, such as for a medium voltage switch, having a first movable plate in form of a round yoke, an actuating shaft and a lower smaller second movable plate in the form of a lower smaller yoke which is fixedly spaced apart from the first movable plate and arranged at an opposite end of the core. A damping pad for mechanical damping is inserted between the core of the magnetic actuator and the small yoke.
However, the thickness of damping pads is generally too large to generate the required force to keep the system, for example, the magnetic actuator and external devices like one or more vacuum interrupters, fixed in an OPEN or OFF position. Generally, the required force in the OFF position is generated by the opening spring. The opening spring will generate the highest force in the ON position. Since the magnetic actuator is generally not able to magnetically generate its own locking force for the OFF position, the opening spring has to be designed in a way that it also helps to generate the locking force in the OFF position. Consequently, the mechanical energy for charging the opening spring during the closing operation is relatively high, and higher than required for obtaining the desired opening speed.